Use of Lime in the Fish Pond

Introduction

Liming is considered as one of the most important steps in pond preparation and treatment. In most of the cases, lime has a great contribution to water quality improvement. So, its use is very frequent in aquacultural practices. Lime can be used as a very good conditioner in the pond. After the pond is ploughed; clear and smooth lime should be used as a conditioner in the pond. Lime also plays an important role in the improvement of pond sanitation. Liming also increases the productivity of the fish pond. In order to promote the healthy growth of fish in the pond, the presence of phytoplankton is very much important. Various nutrient components present in the pond soil, control the growth and survival of different phytoplankton. To make these nutrient components usable, application of lime in the fish pond is very much important.

Functions of lime in the fish pond

The main function of the lime in the fish pond is to reduce the acidity of the soil and water. Other accessory functions of lime in the fish pond are:

To increase the natural food in the pond, this is essential for the better growth and survival of fish. Lime accelerates the process of degradation of organic matter in the pond, so that amount of usable nitrogen in the pond increased rapidly. As a result, natural food for fish grows adequately and sufficiently in the pond.
To increase the amount of usable phosphate in the pond. This is necessary for the growth of phytoplankton. The amount of usable phosphate in the fish pond largely depends upon pH of the soil. If this pH of the soil is in the range of 6.5-7.5, then the amount of usable phosphate in the pond is good. In the case of excessive acidic water, especially when the pH of the soil, is lower than 6.5, the amount of usable phosphate in the pond becomes very low. The main reason for this phenomenon is that most of the phosphate combines with iron and aluminum, so plant usable phosphate becomes extremely low. Application of lime in the fish pond, reduce the acidity of the soil of the fish pond. As a result of that, phosphate becomes free and become usable by plants.
Use of lime in the pond increases the amount of alkalinity in the water which acts as a So, applications of lime in the pond maintain the proper balance of pH of water between morning and afternoon and create the optimum condition for fish culture.
As lime contains calcium, so this increases the productivity of the pond through the application of lime.
Lime helps to cure some fish diseases through its extra alkaline characteristics.
Lime increases the oxygen content of the pond water by changing physical conditions of the water.
Lime increases the transparency of the water.
Lime decreases the amount of toxic gases in the pond.

The optimum amount of lime used in the pond

Amount of the lime to neutralize the pond water largely depends upon the pH of the soil and water of the pond. If the acidity of the pond bottom soil increases, the amount of lime for neutralization also increases. If pH of the pond is neutral, then the amount of lime required also decreases. The optimum amount of lime used in the pond largely depends upon the nature of the soil of the pond.

pH of the soil 40-50: amount of lime should be 2000 kg/ha/yr.
pH of the soil 51-65: amount of lime should be 1000 kg/ha/yr.
pH of the soil 66-75: amount of lime should be 500 kg/ha/yr.
pH of the soil 76-85: amount of lime should be 200 kg/ha/yr.
pH of the soil >86: amount of lime should be nil.

Application of lime

The first step of fish culture is pond preparation. So, before monsoon, we should properly spread lime in the pond.

If we have to mix lime directly with water, then first lime should be mixed in a separate pot before 3-4 hours of application. Then, the solution should spread in a different part of pond water.

Proper application time of lime: Optimum time for application of lime in the water is early morning as water PH becomes very low at this time.

Types of lime and their effectiveness

Calcium oxide or quick lime:

Chemical formula: CaO
Nature: This lime produces heat when it mixes with water. This lime very rapidly increases the PH of soil and water.
Effectiveness: This lime is very much effective in those ponds which are highly acidic. This lime is very much effective in the prevention of fish diseases.

Calcium hydroxide or hydrated lime:

Chemical formula: Ca(OH)₂
Nature: Acidity neutralizing power is less than that of quick lime. This lime produces less heat than quick lime.
Effectiveness: Use of this lime in the pond is very less.

Calcium carbonate:

Chemical formula: CaCO₃
Nature: Acid neutralizing power is very much less than that of other lime. This lime does not produce heat when it mixes with water.
Effectiveness: As this lime does not increase the ph of the pond rapidly, so it is suitable to apply in the alkaline pond where pH of the pond water varies between 8-8.5. Other benefits of the application of lime are also extracted from the lime.

Dolomite:

Chemical formula: CaMg(CO₃)₂
Nature: Acid neutralizing power is very less. This line also contains magnesium apart from calcium.
Effectiveness: This lime increases the amount of magnesium in the water, which is necessary for the nutrition of the plant. Though its use in sweet water is very low, we can get benefit if we use it after mixing with other lime.

Conclusion

The main objective of the liming is to increase the pH of the water of the fish pond. As a result of that water becomes purified from suspended mud and other particles and increase the light available to the plants. Immediately after application of fertilizer, if liming is done, then it may reduce phosphorus from water, which in turn prevents the development of phytoplankton bloom. But the application of lime in the pond also has some drawbacks. Liming is one of the oldest methods of water softening, which demands a very high level of keenness. These processes of liming also exhibit some harmful residues for the environment. Only wise application and careful disposal of the residue can be the best solution to this problem. Otherwise, the toxic residuals may flow to the rivers and soils thus, affecting its acidity and causing great harm to the society.

Author - Satarupa Ghosh

Ph.D. Scholar, Aquatic Environment Management Department, West Bengal University of Animal and Fishery Sciences, Kolkata, West Bengal-700037, India